Originally Posted by 4.0l sahara
I don't think a fan clutch would cause it to rev.
But I don't really know.
That doesn't sound like the fan clutch. When the fan clutch locks up, the engine has to work harder because it is turning the fan with it's own power all the time. You'll notice a big drop in pick up and particularly on the top end when the fan is locked up.
It's easy to tell if the fan clutch is locked up. Pop the hood and try to move the fan by hand. If it doesn't spin free of the engine, it's locked.
Don't do it with it running. I know I don't have to tell you this, but some people, you never know.